ATHENS, Nov 12 (Reuters) - Greece has told shortlisted investors to submit final bids for a majority stake in its biggest oil refiner Hellenic Petroleum by January, two sources close to the sale said on Monday, pushing the deadline back from November.

Greece, which is selling assets as part of a deal with international lenders, has delayed the deadline several times after Glencore Energy and Vitol Holding were shortlisted to bid for the 50.1 percent stake in the summer.

The market value of the stake is now almost 1.2 billion euros ($1.35 billion), according to Refinitiv's Eikon data.

A source had previously said it expected final bids for the stake "towards the end of November". But two sources close to the sale said the new deadline was in January.

The state has been awaiting a decision by the securities regulator on whether the prospective buyer will have to make a mandatory offer to buy the remaining shares.

Charalampos Gotsis, chairman of the regulator Hellenic Capital Market Commission, told Reuters the commission had decided last week that the winner would not have to make a mandatory offer.

He said Greek privatisation agency HRADF "will be notified tomorrow morning", or Tuesday, about the decision.

The government has raised about 5 billion euros from state asset sales under three international bailouts since 2010.

The country exited the last rescue programme in August but has agreed with lenders to raise another 3 billion euros from asset sales by next year, including Hellenic, in a bid to attract more investment and cut its debt.

The 50.1 percent stake in Hellenic that is being sold comprises a 20 percent stake held by the government and a 30 percent stake held by privately owned Paneuropean Oil.

The government and Paneuropean Oil will each retain a 15 percent stake in Hellenic.